fixes #17 - adding scrollbar to long dropdown menu
fixes #20 - updating period only if it's not already set
refs #23 - override graphite_url per dashboard

* you can now specify the graphite_url in your dashboard
  and it will override the default
revert unnecessary change
Merge pull request #24 from kenhub/override_graphite_url

Allow overriding graphite_url per-dashboard
added CNAME for giraffe.kenhub.com